I saw that it fails when you remove all icons from the dock, but, we have other problem here:

https://github.com/mozilla-b2g/gaia/blob/master/apps/homescreen/js/dragdrop.js#L286

please could you add it as well? It is very simple but very useful :)

```js
if (lastIcon  && y > lastIcon.getTop() && draggableIcon !== lastIcon) {
```
Thanks for it